This invention pertains generally to optical seekers, and more particularly to seekers of such type having improved resolution characteristics through extended ranges of gimbal angles.
The numerical advantages in armored vehicles enjoyed by potential enemy forces and the concomitant threat of a massive armor attack has led to the development of so-called "smart" anti-armor projectiles that are capable of distinguishing between targets and are then automatically guided to a selected target. One known type of smart projectile, incorporating an infrared (IR) seeker, is launched from a cannon or howitzer removed from the forward edge of the battle area. In the terminal phase of the flight of such a projectile the IR seeker searches for, and acquires, a single target even though countermeasures may have been taken by the enemy. Obviously, then, the IR seeker must be adapted (i.e. "g-hardened") to survive the large acceleration (the high-g environment) associated with launching from a cannon.
One known type of g-hardened IR seeker, generally referred to as an optical "free gyro" (meaning free gyroscope) seeker, employs a hard coated spherical gas bearing to survive the high-g environment at launch. While the hard coated spherical gas bearing enables the optical free gyro seeker to survive high-g loads, it restricts the gimbal angle freedom to 15 degrees, thereby unduly limiting the field of view of the seeker. Furthermore, in such a seeker the refrigerated detector unit is "body-fixed" (meaning it moves relative to its associated mirrors or lenses) with the result that resolution is degraded as the gimbal angle is increased.
Obviously, in a stand-off weapon system the effects of ballistic dispersion as well as other environmental conditions, as, for example, wind and rain, will have an adverse impact on the circular error of probability (CEP) of the system. It follows, therefore, that the effectiveness of such a stand-off weapon system will be enhanced if the total field of view and resolution of the projectile seeker are augmented to permit the search for and acquisition of targets over a broader area.